Method and apparatus for fabricating double-layer, welded grid bodies

ABSTRACT

A method and apparatus for fabricating double-layer, welded grid bodies which consist of grids located opposite one another and web wires holding these grids apart at a distance, in which method and installation, to fabricate grid bodies in the form of annular sections, the two grids, at a mutual distance corresponding to the desired thickness of the grid body, are moved forwards concentrically to one another and in a vertical position along concentric circular feed paths, and, after the web wires, fed from the outside of the path, have been welded, preferably in pairs, to the grids, the finished grid body is removed from the outside of the path.

The invention relates to a method of fabricating double-layer, weldedgrid bodies which are bent in a circular-arc shape and which consist ofgrids located opposite one another comprising longitudinal and crosswires crossing one another and welded at the intersections and ofstraight web wires which hold the grids apart at a predetermined mutualdistance and are welded at each end to a wire of one of the two grids,in which method the grids are bent and are arranged at a distance fromone another, whereupon the web wires are inserted from the outside ofthe grids into the intermediate space between the grids, and each webwire is welded to the adjacent wires of the grids. Furthermore, theinvention relates to an installation for performing the method.

BACKGROUND OF THE INVENTION

German Offenlegungsschrift 3,148,939 discloses a method of fabricatingreinforcement bodies for concrete structural parts, in which methodcylindrical wire baskets for reinforcing ferroconcrete pipes areconnected to one another by web wires. The cylindrical wire baskets arefirst supported with a horizontal axis in such a way that the axes ofthe wire baskets first of all do not coincide and the wire baskets arethus not concentric. A spacer is then fed horizontally in the directionof the theoretical centre point of the reinforcement body to befabricated and is welded to the wires of the cylindrical wire baskets.After the wire baskets have been appropriately turned upwards, thefollowing spacers are welded in one after the other. In the process, thetwo wire baskets move further and further apart from their initialposition, which is characterized by a common contact point, until theconcentricity of the two wire baskets is obtained. In this fabricatingmethod, the concentricity is obtained only after a sufficiently largenumber of spacers have been welded in, since only a large number ofspacers distributed at the periphery are able to carry the weight of theinner or outer wire basket not supported by the rollers or the drum.This known procedure is not only relatively complicated but has inparticular the disadvantage that the spacers as well as their weldlocations on the wire baskets are subjected to considerable bendingstress. In addition, the known procedure can only be applied to wirebaskets which consist of complete circles but not to grid bodies ofannular sections, for only wire baskets of complete circles aredimensionally stable in such a way that they can be worked withoutworkpiece-dependent mechanisms and can be moved into a concentricposition by simple turning after the spacers have been welded in.

SUMMARY OF THE INVENTION

The object of the invention is to create a method of the type specifiedat the beginning and an installation for performing the method withwhich double-layer, welded grid bodies bent in a circular-arc shape canbe fabricated in a simple manner in a continuous operation, which gridbodies consist of annular sections and their spacers are stress-free.

The method according to the invention has the features from that, tofabricate grid bodies in the form of annular sections, the two grids, ata mutual distance corresponding to the desired thickness of the gridbody, are moved forwards concentrically to one another and in a verticalposition along concentric circular feed paths, and that, after the webwires have been welded, preferably in pairs, to the grids, the finishedgrid body is removed from the outside of the path.

This procedure enables grid bodies of annular sections havingstress-free spacers and weld locations to be satisfactorily fabricatedin a continuous operation. According to the invention, the concentricityof the grids is accurately defined from the beginning in particular as aresult of the circular feed to which the grids and the grid body aresubjected in a definite manner.

The grids are preferably fed in the form of prefabricated grid matswhich, before they are arranged on the circular feed paths, are bent inaccordance with the path radius.

The subject-matter of the invention is also an installation or apparatuswhich is intended for performing the method and has feed paths for gridslocated opposite one another, a grid feeding station allocated to thefeed paths, and a web-wire feeding station which is arranged to the sideof the feed paths and has web-wire feeding means whose wire feed routesrun across the feed paths, in which arrangement, a welding device havingwelding tongs and intended for the welding of the free wire ends to onegrid is provided on the other side of the feed paths in alignment withthe wire feed routes, and a welding device having welding tongs andintended for welding the cut ends of the web wires to the other grid isprovided on this side of the feed paths downstream in the feeddirection; this installation is characterized according to the inventionin that the feed paths, in accordance with the bending radius of thegrid body to be fabricated, are curved in a circular shape and are alsoarranged concentrically and have a common vertical axis, in that thegrid feeding station allocated to the feed paths is equipped withbending mechanisms for the two grids, in that the web-wire feedingstation downstream from the grid feeding station in the feed directionis arranged on the outside of the feed paths, in that the web-wirefeeding station as well as the welding devices are mounted in such a waythat they can be pivoted towards and away from the feed paths, and inthat a removal station for the finished grid bodies is likewise providedon the outside of the feed paths.

In a preferred embodiment of the invention, in order to work grids fedin the form of endless grid lengths, guide and feed devices for the gridlengths and the grid body as well as, in front of the removal station, amechanism for cutting to length the finished grid bodies are provided onthe feed paths.

Alternatively, in order to work grids in the form of grid mats, agrid-mat clamping mechanism is provided which is guided on the feedpaths and can be moved out of the grid feeding station through theweb-wire feeding and welding stations into the grid-body removalstation.

BRIEF DESCRIPTION OF THE DRAWING

The invention and further features of the same are described in greaterdetail below with reference to exemplary embodiments and the drawings,in which:

FIG. 1A schematically shows in plan view an apparatus for fabricatingbent, welded grid bodies according to the invention, and

FIG. 1B shows the same in an elevation in the direction of arrows B--Bin FIG. 1A;

FIG. 2 shows in plan view a modified embodiment of the apparatusaccording to the invention;

FIG. 3 shows a third embodiment of the apparatus in plan view;

FIG. 4 shows a feeding mechanism for a web wire in plan view;

FIG. 5 shows a side view of the web-wire feeding station of theapparatus;

FIG. 6 shows a part of the welding station of the apparatus according tothe invention;

FIG. 7 shows a mat clamping mechanism in plan view;

FIG. 8 shows an example of a feed and welding diagram, and

FIGS. 9A-9F show sections and elevations of bent, welded grid bodies.

DETAILED DESCRIPTION OF THE DRAWINGS

The double-layer, bent, welded grid body 5, 5' fabricated by theapparatus according to the invention has, according to FIG. 9A-9F, anouter grid mat 3b, consisting of longitudinal wires 54 and cross wires55, an inner grid mat 3a, consisting of longitudinal wires 56 and crosswires 57, and web wires 58 which connect the two grid mats and serve inparticular to stiffen the grid body and as shearing-force reinforcement.As shown in FIGS. 9C and 9F, the web wires 58 can be welded to thelongitudinal wires 54, 56 both below and above the latter.

FIGS. 9A and 9B and respectively 9D and 9E in each case show twosections through the grid bodies 5, 5' in order to show various possiblecombinations for the arrangement of web wires 58 in the grid body. Thesections according to FIGS. 9A and 9D each show a complete complementwith web wires 58, arranged for example at an acute angle to oneanother, as they are conveniently used at the top and bottom margin ofthe grid body for reasons of optimum stiffening of the same. Thesections according to FIGS. 9B and 9E are each taken through a centreportion of the grid body and show further possible combinations for thearrangement of web wires, a web-wire layer which is located deeper orhigher being indicated by broken lines in each case.

The method and the apparatus according to the invention enable gridbodies to be fabricated for different applications with any combinationof web wires; this applies in particular to their number perlongitudinal wire layer, their relative arrangement in the variouslayers, their direction in the grid body relative to the longitudinalwires, and also their diameter, which can likewise vary. Here, as shownin the elevations according to FIGS. 9C and 9F, different combinationsof web wires are also possible within a longitudinal-wire layer.

In addition, FIGS. 9D to 9F reveal that an outer margin of the grid body5' can be designed to have a slope.

An apparatus according to the invention for fabricating the grid body 5bent in a circular-arc shape is shown in FIGS. 1A and 1B. An inner, atfirst flat grid mat 3a which consists of longitudinal wires 56 and crosswires 57 welded to one another is removed from a mat magazine 1a and isgiven the desired bent shape in a bending mechanism 2a. The bendingmechanism 2a can, for example, consist of three drivable rollers whichare connected by means of a chain and whose distance from one anothercan be set, as a result of which the radius of curvature of thelongitudinal wires of the grid mat and thus also of the grid body to befabricated is adjustable within certain limits. If grid mats which areless rigid and have, for example, thin longitudinal wires which caneasily be bent without great expenditure of force are used, and also ifthe grid body to be fabricated has very large radii of curvature, thebending mechanism can be omitted if necessary.

On a mat conveying path 4, the inner grid mat 3a is fed to a matclamping mechanism 7 located in the grid feeding station A and, as willbe described below, is fixed in an upright position in this mat clampingmechanism 7. In the same way, an outer grid mat 3b, which likewiseconsists of longitudinal wires 54 and cross wires 55 welded to oneanother but can differ from the inner grid mat 3a in its construction,is removed from a further mat magazine lb and is given the necessarycurvature in its longitudinal wires in the associated bending mechanism2b. On the mat conveying path 4, the bent grid mat 3b is fed to the matclamping mechanism 7 and is likewise fixed in an upright position in thelatter.

In plan view, the mat clamping mechanism 7 has a circular-sector-shapedframe which is arranged in such a way that it can be moved by means ofwheels 7' on a circular track 6 having a vertical axis and is rotatablyarranged in the track centre 15. In addition, rotatable electric-powerand control lines as well as supply lines for hydraulically andpneumatically operable elements of the mat clamping mechanism 7 arelocated in the track centre 15.

After it has been completely loaded, the mat clamping mechanism 7travels, with the aid of a drive device 8 mounted on its frame, on thetrack 6, defining concentric circular feed paths for the mats, from thegrid feeding station A in the direction of arrow P between a firstweb-wire feeding station 9, arranged outside the track 6, and an innerwelding station 12a, located exactly opposite the web-wire feedingstation 9 inside the track 6, until a shoot-in position for a firstvertical roll of web wires is reached.

At this location, the drive device 8 is stopped and the further cyclicfeed of the mat clamping mechanism 7 is now taken over by a positioningdrive device 14 which is provided in the entry area of the firstweb-wire feeding station 9 and has a drive pinion which is displaceablein the radial direction and can be meshed with a toothed rack of the matclamping mechanism 7.

From supply coils 10, for example via a coil or reel run-off, the webwires 58, by means of feeding mechanisms 11 which each essentiallyconsist of a roller shoot-in device and shears, as will be describedbelow, are shot into corresponding positions at the longitudinal wires56 of the inner grid mat 3a, are cut to length and are welded to thelongitudinal wires 56 of the inner grid mat 3a in the inner weldingdevice 13a.

During the shoot-in action of the web wires 58, the web-wire feedingstation 9, in which feeding mechanisms 11 are arranged in the verticaldirection in accordance with the maximum number of web wire layers to beshot in, and inner welding device 13a, in which welding tongs 42 arearranged in a vertical direction in at least the same number, performthe pivoting movement, shown in the elevation by arrows P', in thedirection of the grid mats 3a, 3b. The pivoting movement of the web-wirefeeding station 9 is effected by a pivot device 38, and the synchronouspivoting movement of the inner welding device 13a is effected by a pivotdevice 52. After the pivoting actions are complete, the web-wire feedingstation 9 as well as the inner welding device 13a pivot back into theirinitial position.

In accordance with the desired arrangement of the web wires, the matclamping mechanism 7 is now fed to the next web-wire feeding station 9and the inner welding station 12a located opposite the latter, where,with the corresponding pivoting movements of the wire feeding station 9and the welding device 13a being performed, web wires are again shot in,cut to length and welded to the inner grid mat 3a.

The next feed steps move the mat clamping mechanism 7 into followingouter welding stations 12b arranged on the outside of the track 6 andhaving corresponding outer welding devices 13b. In these welding devices13b, which, just like the inner welding devices 13a, contain a pluralityof vertically arranged welding tongs 42 and likewise perform a pivotingmovement in the direction of the grid mats 3b into the welding position,the web wires 58 are also welded to the longitudinal wires 54 of theouter grid mat 3b. After the welding operations are complete, the outerwelding devices 13b likewise pivot back again into their initialposition.

It will be understood that, during these feed steps, web wires can befed again by means of the mechanisms 11 and welded on by means of theinner welding devices 13a.

In accordance with the predetermined arrangement of the web wires,further cyclic feeds of the mat clamping mechanism 7 take place so thatweb wires 58 are shot in at the respective positions and are welded onon the inside and on the outside until the grid body 5 is completelyfitted with web wires. In relation to the curve length of the outerframe part 66 of the mat clamping mechanism 7 and to the dimensions ofthe welding stations 12a, 12b, a positioning drive device 14' arrangedat the end of the outer welding station 12b here takes over the furtherfeed of the mat clamping mechanism 7.

As soon as the grid body 5 is finished, the mat clamping mechanism 7,under the action of the drive device 8, travels into a removal station Ein which the finished grid body 5 is removed and is fed to a furtherprocessing means or a stacking means. The empty mat clamping mechanism 7then travels further into the grid feeding station A and the operatingcycle described begins again.

The web-wire feeding station 9 and inner and outer welding station 12a,12b having the corresponding welding devices 13a, 13b, as shown, forexample, in FIG. 1, can each be present in duplicate so that a pluralityof operations can be performed simultaneously and thus the productionspeed of the welding installation can be increased. Here, all web-wirefeeding stations 9 and all welding devices 13a, 13b are individuallycontrollable and only the sequences of movement of the web-wire feedingstations 9 with the allocated, oppositely located inner welding devices13a are coordinated with one another.

It is of course also possible to provide the abovementioned stations 9and 12a, 12b in any number, the maximum possible number in principlebeing limited only by the space requirement for the individual stationsand for the operating sequence of the method, such as the spacerequirement for feeding the grids and removing the grid body.

The individual web-wire feeding stations 9 as well as the inner andouter welding stations 12a, 12b are displaceable relative to one anotherand in the direction of the track 6 on a base plate (not shown) so thatthese stations, in their position relative to one another and towardsthe track, can be adapted to the geometry of the grid bodies to befabricated.

To increase the productivity of the installation, a plurality of matclamping mechanisms 7 of the same type can be used, as is likewise shownin FIG. 1, all mat clamping mechanisms successively performing theindividual steps of the method such as the loading with grid mats, theshooting in and welding of the web wires and the removal of the finishedgrid body.

FIG. 2 shows a further exemplary embodiment of an installation accordingto the invention, which can also be combined with the exemplaryembodiments of installations according to the invention shown in FIGS. 1and 3. To fabricate grid bodies 5 having different radii of curvature,as are necessary, for example, for the reinforcement of tunnel tubes ofdifferent sizes, two tracks 6₁ and 6₂, for example, having a verticalaxis are provided, the radii of curvature of the tracks and thedimensions of the mat clamping mechanisms being adapted to the radii ofcurvature of the grid bodies. Since the web-wire feeding stations 9 andthe welding stations 12a, 12b are constructed so as to be in a fixedposition if possible, the centre points of the tracks 6₁, 6₂, differingin radius, and thus the centres 15₁, 15₂ of rotation of the mat clampingmechanism 7₁, 7₂ are displaced relative to one another in such a waythat the tracks 6₁, 6₂ touch in the first welding position, which islocated between the first web-wire feeding station 9 and the first innerwelding station 12a. To fabricate grid bodies 5 having a smaller radiusof curvature, the centre 15₁ of rotation applicable to a mat clampingmechanism 7₁ having a large radius is shifted in the direction of thefirst welding position so that a centre 15₂ of rotation for a matclamping mechanism 7₂ having a smaller radius is obtained. So as not todisturb the sequence of movements, the mat clamping mechanism 7₁ isremoved and only the mat clamping mechanism 7₂ with the associated track6₂ having the smaller radius of curvature is used.

In addition, the second web-wire feeding station 9 and the weldingstations 12a, 12b are if necessary displaced in the direction of thetrack 6₂.

Furthermore, a further exemplary embodiment of a feeding device 11' withwhich only individual stiffening wires can be fed is shown in FIG. 2 inthe second web-wire feeding station 9.

In a further embodiment of the invention shown in FIG. 3, the gridbodies can be fabricated by a continuous method of fabrication. Here,from a supply roller 16a, an endless inner grid length 3a, and, from afurther supply roller 16b, an endless outer grid length 3b are advancedfrom the outside and tangentially up to the track 6 and correspondingpreforming stations 2a and 2b which, in this exemplary embodiment, arelocated directly in the area of the track 6. The bending stations 2a, 2bare driven accordingly and draw off the grid lengths in cycles from thesupply rollers 16a, 16b and feed the grid mats 3a, 3b, which are nowbent. The grid mats 3a, 3b are guided along the track 6 by means ofadditional guide rollers 17, which are arranged on both sides along thefeed path of the inner and outer grid mats in the feed direction infront of the welding stations 12a, or by means of guide rollers 17'which are in each case arranged on both sides outside the grid bodyalong the track inside and, in the feed direction, behind the weldingstations 12b. The guide rollers 17' which lie behind the weldingstations 12b can be provided with an additional feed drive (not shown)in order to feed the finished grid body 5, cut off from the line ofmaterial by means of shears 20, in an accelerated manner to the removalstation E.

A further embodiment of a feeding mechanism for cut-to-length web wiresis shown in FIG. 3, it also being possible for this web-wire feedingmechanism to be combined with the installations according to theinvention which are shown in FIGS. 1 and 2. By means of this feedingmechanism, stiffening wires 58 already cut to length are shot from thesupply magazines 18 by means of web-wire feeders 19 into thecorresponding position into the grid bodies.

FIG. 4 shows an embodiment of a mechanism 11 according to the inventionfor simultaneously feeding two web wires running in a convergent mannerat an acute angle. This mechanism is also suitable for feeding only asingle web wire if, for example, only one feeding channel is used.

The web wires 58 enter via guide nozzles 21 into the feeding device 11,pass through vertically arranged alignment rollers 22 and horizontallyarranged alignment rollers 23 in which the web wires 58 are straightenedand then pass into cutting nozzles 24 which, together with the cuttingblade 25, are located on a cutting beam 26. Web wires 58 are fed bymeans of feed wheels 27 which are arranged between the alignment rollers22 and 23 and are pressed against the web wires 58 by means of aclamping lever 29 and an eccentric lever 30, in which arrangement animproved frictional connection can be obtained by suitable design of therunning surfaces, such as, for example, toothing or knurling.

The length of the web wire to be shot in is measured by means of ameasuring wheel 28, connected to a shaft 33 of the feed wheels 27, forexample by means of toothed belts, and a measuring transducer 35. Afterthe target length is reached, the feed is stopped, the welding tongs 42of the inner welding devices 13a are closed in order to fix the web wire58 on the longitudinal wire 56 of the inner grid mat 3a, and the webwire 58 is cut off from the line of material by means of the cuttingblade 25 vertically movable on the cutting beam 26.

Drawn in FIG. 4 is the shoot-in angle α of the web wires, defined as theangle between the respective shoot-in path of the web wires and therespective normal to the tangential plane to the inner bent grid mat atthe location of the respective welding positions at the longitudinalwires 56 of the inner grid mat.

As can be seen from FIG. 5, a plurality of feeding devices 11 or 11',each of which can be vertically adjusted and secured in position bymeans of a clamping device 31, for web wires are arranged vertically ina row in the web-wire feeding station 9, the feed wheels 27 of eachindividual feeding device being arranged in such a way that they can bevertically adjusted and locked in position on the common shaft 33, whichcan be driven by a drive device 34.

The clamping levers 29 on the eccentric lever 30 can be replaced, forexample, by hydraulically operable clamping cylinders 32 so that the webwires 58 can be controlled for shooting in or not shooting in. Thecutting movement of the cutting blades 25 is performed by two cuttingcylinders 36 which can be controlled alternately.

The aforementioned pivoting movement of the wire feeding station 9(arrow P'), which takes place at the same time as the feed of the webwire 58 in the direction of the grid mats 3a, 3b and back again into theinitial position after the welding and cutting operations are complete,is performed by means of a crank-pivot drive 37 and a pivot device 38formed from guide links.

For the purpose of changing the shoot-in angle α of the web wires whichis indicated in FIG. 4, the wire feeding station 9 can be connected to abase plate 41 in such a way as to be pivotable about the pivot axis 39.If necessary, the shoot-in angle α can also be changed by pivoting thecutting beam 26 about its axis 40.

FIG. 6 shows an exemplary embodiment for the welding stations 12a, 12b.A plurality of welding tongs 42 having welding electrodes 43 arearranged in such a way that they can be vertically adjusted and securedin position on a welding-tongs stand 44. The welding tongs 42 areactuated by means of welding cylinders 45, in which arrangement thewelding pressure can be adapted to the diameters of the wires to bewelded.

The requisite welding current, likewise adapted to the diameters of thewires to be welded, is supplied from welding transformers 49 to bus-bars47 via conduction bands 48 which permit the pivoting movement of thewelding device 13a, 13b, which essentially consists of the welding-tongsstand 44, the welding tongs 42 and the bus-bars 47. From the bus-bars 47the current is fed to the welding tongs 42 via flexible electric powercables 46.

The number and the circuit wiring of the welding transformers 49 and ofthe bus-bars 47 as well as subsequently of the electric tongs 42 isselected in accordance with the number and cross-sections of the wiresto be welded in the different combinations 54, 58 and 56, 58.

The welding electrodes 43 are preferably designed to be of large area.Consequently, as indicated in the feed and welding diagram according toFIG. 8, a plurality of stiffening wires 58 can also be welded at thesame time as the corresponding longitudinal wires 54, 56 and, if needbe, slight deviations in the positioning of the web wires 58, caused forexample by different shoot-in angles α, can be tolerated.

As already mentioned, the welding device 13a, in synchronism with theshoot-in feed of the web wires, and the welding device 13b, by means ofa crank-pivot drive 51 and a pivot device 52 formed by guide links,perform a pivoting movement (arrow P') into the welding position and,after the welding is complete and the welding tongs 42 have opened, apivoting movement in the opposite direction back into the initialposition.

For the purpose of changing the welding position on the longitudinalwires, due to any change which may arise in the shoot-in angle α of theweb wires, the welding stations 12a, 12b are pivotably mounted on a baseframe 53 about a pivot axis 50.

In the representation of the mat clamping mechanism in FIG. 7, thecentre 15 of rotation, the base frame and the drive 8 are omitted andonly the elements on the bottom, curved part 66 of the mat clampingmechanism 7 are shown, which elements are necessary for the positioningand fixing of the grid mats 3a, 3b inside the mat clamping mechanism 7.

In the grid feeding station A of the welding installation, to load themat clamping mechanism with grid mats, first of all mat positioningdevices 59, of which there are several in the mat clamping mechanism,for the longitudinal wires 54, 56 are moved along guides 60 by means ofactuating elements (not shown), such as, for example, pneumaticcylinders, and inner mat centering means 61a, of which there arelikewise several, for the cross wires 57 are moved by a pivotingmovement into their working position, as a result of which the innergrid mat, with its longitudinal wires 56 and its cross wires 57, isexactly determined in its position in the mat clamping mechanism 7.

After it is inserted, the inner grid mat 56, 57, by means of pivotableinner clamping grips 62, of which there are likewise several, is clampedin place against oppositely located fixing stops 63 of the clampinggrips. As soon as the clamping grips 62 are closed, inner mat centeringmeans 61a open and outer mat centring means 61b, of which there arelikewise several, pivot into their working position, as a result ofwhich, together with the mat positioning devices 59, the position of theouter grid mat, with its longitudinal wires 54 and its cross wires 55,in the mat clamping mechanism 7 is now also exactly determined.

After the outer grid mat 54, 55 is inserted, the same is fixed by outerclamping grips 64, of which there are several, swinging in againstoppositely located outer mat stops 65, which can likewise be swung in.

As soon as the clamping grips 64, 65 are closed, the outer mat centeringmeans 61b open again and the mat positioning devices 59, which are nolonger required, are lowered into their initial position.

The clamping grips 62, 64, 65 are closed in groups, which operation ispreferably started at the margins of the grid mats so that distortion ofthe grid mats is avoided.

The number of mat positioning devices 59, mat centering means 61a, 61band also inner clamping grips 62 plus the fixing stops 63 and outerclamping grips 64, 65 depends on the length and inherent rigidity of theinner and outer grid mats.

The clamping grips 62, 64, 65 as well as the fixing stops 63, for thepurpose of fixing the two uppermost longitudinal wires 54, 56 of thegrid mats, are also present on an upper, curved part 66' of the matclamping mechanism 7 and are controlled and actuated in synchronism withthe corresponding elements on the lower curved part 66 of the matclamping mechanism.

In the removal station E of the welding installation, the finished gridbody 5 is seized by means of gripping attachments which are extendedfrom the outside of the track 6, and the clamping grips 62, 64, 65 openand release the grid body for removal.

For the purpose of adapting the individual elements of the mat clampingmechanism to the different geometry of various grid bodies to befabricated, in particular to the different spacings of the longitudinaland cross wires of the grid mats, the corresponding elements of the matclamping mechanism are attached in such a way that they can be securedin position, are if necessary vertically adjustable and are horizontallydisplaceable on the lower and upper curved parts 66 and 66' respectivelyof the mat clamping mechanism 7.

The curve length of the curved parts 66, 66' of the mat clampingmechanism 7 can be adapted to the grid bodies to be fabricated, but itis also possible, while appropriately positioning the positioning,centring, clamping and fixing elements 59, 61a, 61b, 62, 63, 64, 65 inthe mat clamping mechanism 7, to arrange grid mats which are shorterthan the curve length of the curved parts 66, 66', as shown, forexample, in FIG. 1, or also to arrange more than one grid mat pair 3a,3b.

In the feed and welding diagram according to FIG. 8, an exemplaryembodiment for the welding of the web wires at the upper margin R of agrid body as well as in two centre layers M of this grid body is shownin perspective representation. In this schematic representation, thewelding electrodes 43 are indicated in a square shape, but they can haveany shape suitable for simultaneously welding a plurality of web wires58 to the longitudinal wires 54, 56.

Furthermore, the various feed and welding cycles I-IV of the weldinginstallation are shown. The arrows shown represent the shoot-indirections of the web wires at the appropriate positions.

It will be understood that the welding installation, in view of thecomplex operating sequence of the method, is conveniently equipped withan automatic control system which monitors, coordinates and controls thesequences of movement of the individual components of the installationand also provides at the right moment the adjustable parameters,necessary for fabricating different grid bodies, for performing themethod according to the invention, such as, for example, the grid bodytype, the choice and number as well as the shoot-in angle of the webwires in the various layers of the grid body, the step length and thenumber of feed cycles, etc.

The exemplary embodiments described can be modified in various wayswithin the scope of the general concept of the invention, in particularwith regard to the number of web-wire feeding and welding stationsconnected one behind the other.

We claim:
 1. Method of fabricating double-layer, welded grid bodies, which are bent in a circular-arc shape and which have grids located opposite one another comprising longitudinal and cross wires crossing one another and welded at the intersections and of straight web wires which hold the grids apart at a predetermined mutual distance and are welded at each end to a wire of one of the two grids, in which method the grids are bent and are arranged at a distance from one another, whereupon the web wires are inserted from the outside of the grids into the intermediate space between the grids, and each web wire is welded to the adjacent wires of the grids, characterized in that, to fabricate grid bodies in the form of annular sections, the two grids, at a mutual distance corresponding to the desired thickness of the grid body, are moved forwards concentrically to one another and in a vertical position along concentric circular feed paths, and in that, after the web wires have been welded, preferably in pairs, to the grids, the finished grid body is removed from the outside of the path.
 2. Method according to claim 1, characterized in that the grids are fed in the form of prefabricated grid mats which, before they are arranged on the circular feed paths, are bent in accordance with the path radius.
 3. Method according to claim 1, characterized in that the grids are fed to the feed paths in the form of endless grid lengths and, when they are inserted into the feed paths, are bent in accordance with the feed-path radius.
 4. Apparatus for a method for fabricating double-layer, welded grid bodies which are bent in a circular-arc shape and which have grids located opposite one another having feed paths for grids located opposite one another, a grid feeding station allocated to the feed paths, and a web-wire feeding station which is arranged to the side of the feed paths and has web-wire feeding means whose wire feed routes run across the feed paths, in which arrangement, a welding device having welding tongs and intended for the welding of the free wire ends to one grid is provided on the other side of the feed paths in alignment with the wire feed routes, and a welding device having welding tongs and intended for welding the cut ends of the web wires to the other grid is provided on this side of the feed paths downstream in the feed direction, characterized in that the feed paths (6) in accordance with the bending radius of the grid body to be fabricated, are curved in a circular shape and are also arranged concentrically and have a common vertical axis, in that the grid feeding station (A) allocated to the feed paths is equipped with bending mechanisms (2a, 2b) for the two grids (3a, 3b), in that the web-wire feeding station (9) downstream from the grid feeding station (A) in the feed direction is arranged on the outside of the feed paths, in that the web-wire feeding station (9) as well as the welding devices (13a, 13b) are mounted in such a way that they can be pivoted towards and away from the feed paths, and in that a removal station (E) for the finished grid bodies is likewise provided on the outside of the feed paths.
 5. Apparatus according to claim 4, characterized in that, inside the group of feed paths, at least one further group of circular feed paths having a smaller radius is provided to fabricate grid bodies having different curvature, the feed-path groups touching one another in the area of the web-wire feeding station (9).
 6. Installation according to claim 4, characterized in that, in order to work grids fed in the form of endless grid lengths (3a, 3b), guide and feed devices (17, 17') for the grid lengths and the grid body as well as, in front of the removal station (E), a mechanism (20) for cutting to length the finished grid bodies are provided on the feed paths (6).
 7. Installation according to claim 4, characterized in that, in order to work grids in the form of grid mats (3a, 3b), at least one grid-mat clamping mechanism (7) is provided which is guided on a track (6) defining the feed paths and can be moved out of the grid feeding station (A) through the web-wire feeding and welding stations (9; 12a, 12b) into the grid-body removal station (E).
 8. Installation according to claim 7, characterized in that the clamping mechanism (7) has a movable frame (66; 66') which in plan view is curved in accordance with the circular track (6), and a rotary mounting (15) for the frame (66) is provided in the centre of the track (6).
 9. Installation according to claim 7, characterized in that, when there are a plurality of circular tracks (6₁, 6₂), the rotary mounting (15₁, 15₂) for the frame (66; 66') of the clamping mechanism (7) is adjustable along a track diameter.
 10. Installation according to claim 4, characterized in that the web-wire feeding station (9) has a plurality of web-wire feeding mechanisms (11) which are arranged one above the other in the vertical direction, can be adjusted relative to one another in this direction and secured in position, and are preferably provided with two web-wire feeding means each whose web-wire feed routes run in opposite directions at an angle to the tangential plane of the track (6), and in that the welding tongs (42) allocated to the web-wire feeding mechanisms (11) are likewise arranged in such a way that they can be adjusted in the vertical direction and secured in position.
 11. Installation according to any of claim 4, characterized in that the web-wire feeding station (9) and the welding stations (12a, 12b) are mounted in such a way that they are displaceable on a base plate relative to one another and towards the feed paths (6) and, preferably for the purpose of changing the angle at which the web wires are fed to the feed, are pivotable about a vertical axis (39 and 50 respectively).
 12. Installation according to claim 4, characterized in that each welding device (13a, 13b) essentially consists of a welding-tongs stand (44), the welding tongs (42) and the bus-bars (47), which are mounted in the welding station (12a, 12b) in such a way that they are pivotable by means of a pivot mounting and a pivot drive (51, 52) towards the grid feed paths (6).
 13. Installation according to claim 4, characterized in that in each case two or more web-wire feeding stations (9) and allocated welding stations (12a, 12b) connected one behind the other in the feed direction of the grids are provided.
 14. Installation according to claim 4, characterized in that the web-wire feeding station (9), or at least one web-wire feeding station (9), is equipped with web-wire feeding mechanisms which can be loaded with web wires, cut to length beforehand, from a magazine (18) by means of a feeder (19).
 15. Installation according to claim 6, characterized in that the clamping mechanism (7) is equipped with a drive device (8) which effects the drive from the grid feeding station (A) up to the first welding station (12a) and from the second welding station (12b) into the removal station (E) as well as from the latter further into the grid feeding station (A), in that the rack of the web-wire feeding station (9) has a further drive device (14) which can be set in drive connection with the clamping mechanism (7) and takes over the cyclic feed of the clamping mechanism essentially through the first welding station (12a), and in that the frame of the second downstream welding station (12b) has a third drive device (14') which can be set in drive connection with the clamping mechanism (7) in order to convey the latter in cycles essentially through the second welding station.
 16. Installation according to any of claim 6 characterized in that positioning and centering devices (59, 61a, 61b) for the longitudinal and cross wires of the grids as well as devices (62-65) for clamping the grids in place are provided on the frame (66; 66') of the mat clamping mechanism (7). 